Method of impregnating multilayer paper insulation



METHOD OF IMPREGNATING MULTILAYER PAPER INSULATION Nov. 15, 1955 c. G.MUNTERS 2 Sheets-Sheet 1 Filed 00 wmw k NQQ I A TTORNEY Nov- 1 1955 c.G. MUNTERS 2,723,923

MPREGNATING MULTILAYER PAPER INSULATION METHOD OF Filed Oct. 2, 1947 2Sheets-Sheet 2 ATTORNEY im l mxw United States Patent METHOD OFIMPREGNATIN G MULTILAYER I PAPER INSULATIGN Carl Georg Munters,Stocksund, Sweden Application October 2, 1947, Serial No. 777,534

1 Claim. (Cl. 117-102) This application is a continuation in part of myapplication Ser. No. 396,014 filed May 31, 1941, now abandoned.

The present invention in one of its principal aspects relates to thetreatment of material with a desired treating agent. More specificallythe invention relates to the treatment of fibrous material with animpregnating agent and still more particularly the invention relates tothe manufacture of impregnated insulating material of the multi-ply typeform of paper sheets impregnated with a bituminous impregnating agent.In another of its aspects the invention relates to improved methods forthe recovery of a vaporizable liquid solvent or other vehicle employedas a carrier for the treating or impregnating agent applied to thematerial. a

Since the invention is particularly applicable and useful for theproduction of insulation of superior quality of the above describedkind, it will hereinafter be described by way of example but withoutlimitation, insofar as certain aspects of the invention are concerned,as employed for that use, it being understood that the scope of theinvention in its several aspects is defined in the claim appendedhereto.

Multi-ply insulating materials made of non-impregnated paper are lesssatisfactory when subjected to moisture, as is particularly the case inrefrigerating plants, it being understood that the paper loses itsstrength when the moisture content thereof exceeds a certain value. Ifthe various paper plies are connected with one another by gluing, forinstance by means of water glass or other binding agents soluble inwater, which is most frequently the case, the risk of the insulationbeing destroyed or collapsing after a certain time of use is increasedstill more. Furthermore, the non-impregnated paper insulation issubjected to decomposition and molding, and so forth.

It has been proposed, therefore, to impregnate paper with a bituminousagent, such as asphalt. This class of impregnating agents hasexceedingly good properties for the purpose in view and, besides, it iscomparatively cheap. It has been found, however, that the manufacture ofpaper insulation impregnated with such substances involves certaindifiiculties. Thus, where paper impregnated with bitumen is corrugatedbetween toothed rollers, it may occur that the paper ply is caused tostick to the rollers, which incurs the risk of its becoming torn.Contributing to this is also the fact that the paper must be heated inconjunction with the corrugation to a comparatively high temperature, inorder that its shape shall be maintained after it has left the toothedrollers. Upon such heating, the bitumen is caused to melt so as tobecome sticky- Certain difliculties are met with in uniting the variousimpregnated paper sheets with each other, particularly so if the bindingis effected with the aid of bitumen. The paper sheets have also beensewn together by means of thread. An insulating unit produced in thismanner does not, however, obtain any satisfactory rigidness andstrength.

The factors, which are determining the efiiciency of a heat insulation,are the following:

(a) Heat transfer by radiation,

(b) Heat transfer by convection,

(0) Heat transfer by conduction in the solid and gaseous substance.

In the case of heat insulation of the particular type according to thepresent application, that is to say a multilayer insulation ofnon-metallic fibrous foils or sheets, it is possible to form the same ina manner such that it has a favourable figure of heat transfer. Here, itis necessary, however, in order to reduce or to eliminate the effect ofthe factors (a) and (b), to space the layers very close. The averagespacing is thus preferably less than 2 mm. The radiation is eliminatedto a great extent by the many layers, and convection of the gas or airin the interior of the insulation is prevented by the small height orcross section of the passages, whereby the air or gas is caused toremain stationary in the same. The conduction in the air (gas) whichfills the passages is given by the figure of conduction thereof, whereasthe conduction in the paper substance depends on the magnitude of thetotal cross sectional area, through which the heat flows. Now, if thepaper of such a multilayer insulation is impregnated, the twofirst-mentioned factors are not influenced whereas the conduction in thesolid substance depends on the quantity of impregnating agent.

To provide an insulation product withstanding a temperature as high aspossible, without the impregnating agent melting, and which is notsticky at ordinary temperature but may be handled conveniently instoring, transport and mounting, it is important that the impregnatingagent have a high melting point. If a unit of paper sheets is in knownmanner dipped into a bath of an agent of this kind, such as bitumen,being heated to the highest temperature which the paper can withstandwithout carbonizing, the agent will still not be sufficiently viscous.The result is that too much agent remains in the numerous passages ofthe insulation, whereby the factor (c) as per above is influencedinsofar as the conduction through the solid substance impairs theefiiciency of the insulation.

It is the general object of one aspect of this invention to provide amethod which takes care of the conditions particularly applicable toinsulations of a multi-ply type to provide a new and improved producthaving highly desirable properties, such for example as a very lowfigure of heat transfer, which may be as little as 0.034 cal./m. h. C,low weight, high resistance to moisture and relatively great rigidityand strength. To this end impregnating agents such as asphalt or thelike which are solid at normal temperatures are employed, and in anotherof its aspects the invention has as a general object the provision ofimproved methods for removing and recovering from the treated materialthe solvents required to apply such impregnating agents, so as to leavethe material in substantially dry state without stickiness and also soas to recover a higher percentage of the solvent employed than hashitherto been possible with prior known recovery methods, thus enablingthe treated material to be produced at low cost because of the highrecovery of the relatively expensive solvent required.

Further objects and advantages of the invention will be apparent fromthe following description considered in connection with the accompanyingdrawings, which form a part of this specification, and of which:

Fig. 1 is a side view, partly in section, of the upper part of anapparatus for carrying my invention into effect.

Fig. 2 is a perspective in part sectional view of the lower part of saidapparatus and Fig. 3 is a perspective view of a heat insulation.

The apparatus shown in the drawings-is preferably built in two floors.The upper part illustrated in Fig. 1 comprises an impregnating anddrying chamber 16 of rectangular form in a horizontal section. Thischamber is adapted to receive a basket 12 including only two verticalwalls 14, secured at the top to a cover 17.; Secured to the bottom ofthe walls is a grate 16 while an upper grate 18 is movably mountedbetween the walls 14. The space between the grates 16,- 18 and the walls14 is adapted to be filled with units of multi-layer paper insulation.Said units consist as shown in Fig. 3 of a plurality of alternatingplane and corrugated plies 19, 23 which prior to being impregnatedaccording to the invention are united with each other by means of asuitable binding agent, such as water glass. The corrugations areparallel through the whole unit. The binding agent may be applied ontothe corrugations all over the length thereof; a comparatively strongbinding of the various plies being attained thereby; In mostcases it issufiicient, however, to attach the variousplies at points only, asindicated at in Fig. 3. The spacing of two adjacent plane sheets 19 isabout 4 mm. The weight of the paper is preferably between 40 to 65)gr'./m. The units 20 are placed side by side over the whole crosssectional area of the basket with their open ended channels extending inthe vertical direction, and are kept in position by the upper grate 18.The basket 12 with the units 20 is lifted by a handle 21 and placed inthe chamber 10 by a vertical movement until the flanges 22 of the cover17 bent 90 downwardly are supported on the bottom of a liquid seal 24preventing gas from escaping from the chamber.

Connected to the chamber 10 is a circulating system comprising a channel26 communicating with a lower part of the chamber and extending upwardlyto a level above that of the grate 18 when the basket 12 is in theposition shown in Fig. l. The channel 26 is connected to the suctionside of a fan 28. The pressure side of said fan cornmunicates with achannel 38 in which a condenser 32 is disposed. Said condenser has aninlet conduit 34 and an outlet conduit 36 for cooling water having atemperature which may be between 4 to 25 C. in accordance with theseason and climate conditions; The end of the channel is divided intotwo branches 38, 49. The branch chan nel 38 communicates throughchannels 42, 44, 46 with the chamber 10, the last mentioned channelopening laterally into the chamber 10 below the cover 17 and above thegrate 18, as indicated at 48'. The channel 46 has heating elements 50having an inlet 52 and an outlet 54 for a heating medium; such as steam.A channel 56 connects the channel 30 at a point between the fan 28 andthe condenser 32, with the return channel 44. The return flow to thechamber 10 may in part be directed through a channel 53 arranged inparallel Withthe channel 44 and bypassing the heatingelements 56. Valvemembers or dampers 6h, 62, 64' and 66 are arranged in the channels forproviding the various flows through the same as will be explained inthefollowing. A vent pipe 68 to the atmosphere, controlled by a valve 70,-extends from the channel 30 at a point between the fan 28 and thecondenser 32.

The branch channel opens at the bottom of a low temperature condenser72' working with a liquid cooling medium, preferably a brine, such aswater and calciumchloride. The condenser 72 has two vertically spacedgrates 74, 76 carrying layers 78 and 80 of distributing members for thecooling medium, preferably rings of clay of known construction. Betweenthe two grates 74, 76 one or more distributing troughs 82 for thecooling medium are provided, the longitudinal upper edges of which maybe toothed or the like, as at 8 4, to facilitate even distribution ofthe medium over the lower ring layer 78. While the grates 74, 76 and thering layers 78, 80 extend horizontally overthe whole cross section ofthe condenser 72, the trough 82 has less extent at right angles to theplane of the drawing so that the medium flowing over the toothed edges84 is spread as evenly as possible over the layer '78. While thecirculating system above described is closed to the atmosphere thecondenser 72 communicates with a contaiiir 86 haviiig' a ring of holes88 and a passage 90 opening to the atmosphere. On a grate 92 positionedabove the holes 88 there is a layer of ring members 94 of the same kindas the ring member 78, 88. The upper part of the condenser 72 isconnected to the channel 42 by a channel 81 controlled by the valvemember 60. To reduce heat losses by radiation parts of the apparatus,such as the condenser 72, are heat insulated, as indicated at 95.

A refrigerator 26 which may be of any known construction is connectedwith a heat exchanger 98 of wellknown kind through conduits 101), 102;The cooling medium enters the exchanger 98 through a conduit 164 andafter being cooled down to a temperature below 0 0, preferably 15 C. ormore is pumped through a conduit 106 and through a valve 108 to the box82 whereby the distributing rings 78 are soaked by the medium. A branch110 of the pipe 196 opens inthe interior of the air vent container 86above the layer 94 so that also it is soaked by cooling liquid. From thebottom of the container 86 said liquid is conveyed to the box 82 througha P p 2- On the lower floor there are preferably two tanks 114 and 116containing an impregnating agent, such as bitumen or asphalt, and asolvent, such as tri-chloro-ethylene or other chlorinated hydrocarboncompound of the same kind. The bitumen is of a kind being hard andbrittle at normal temperature. The tanks may have an intermediate wall118, dividing them intotwo compartments, each having an upper opening,normally closed by a cover 120. Extending from the lower part of thecompartments of the tank 116 are pipes 121,123, controlled by valves 122and corinected to a pipe 124 through two branch pipes 126 and 128,communicating with the suction and pressure side of a pump 130, drivenby a motor 132, through pipe connections 134 and 136, respectively. Insaid pipes valves 138, 140, 142, 144 and 146 are inserted, ina mannersuch that fluid can be pumped from the pipes 121, 123 to the pipe 124 orvice versa while the pump 136 is rotating in one and the same direction.Likewise,- the two compartments of the tank 114have discharge pipes 148and 150 controlled by valves 152 and connected to the inlet of a pump154 driven by a motor 156. The outlet of the pump 154 communicates withthe pipe 124 through a pipe 158 controlled by a valve 160. I I Thepipe124 opens at the bottom of the channel 26 laterally of the chamber 10.While the impregnating fluid may be fed to the chamber 10 through any ofthe tanks 116 and 114, I prefer to store the fluid in the tank 116. Whenthe chamber 10 is filled to the level 162 which is above the grate 18, alevel control 164' of known construction automatically stops the pump.After the units 29 are impregnated, the excess fluid may flow back tothe tank 116 by gravity, although I prefer to use the pump 139 for thatpurpose; I

Secured to the eiids of the pipes 121,- 123, 148 and 150 in the tanksare disks 166 which carry strainers 168 adapted to prevent any solidparticles from entering the container 10. These strainers can be liftedup for inspec tion and cleansing by rods 17 0.

impregnating liquid may be prepared in the tank 116, pieces of the agentand solvent being for that purpose filled in through the upper openingsof said tank. The solvent is circulated by the pump through the conduit121 or 123,- the conduits 128, 134, 140, 126 and 158,- a conduit 172, avalve 173 and an ejector 174 opening in each compartment of the tank 116and adapted to give the solvent at high speed to facilitate thedissolving of the solid agent pieces. During this operation a valve 176in the pipe 124 is closed. However, I normally store, as stated above,the impregnating liquid in the proper concentration in the tank 116,while new liquid is mixed in the tank 114, the pipe 158 having for thatpurpose branches 178, the ends of which are formed 'as ejectdrs 180. The

latter are in this tank surrounded by tubes 182 open at both ends toimpart turbulence to the liquid. Valves 184 are inserted in the branches178. The liquid can be circulated through the tank by means of the pump154, the valves being adjusted to open connections between the pipes148, 150 and 178, respectively. The liquid is fed over to the tank 116as it becomes consumed in the same.

The two compartments of the tanks 114 and 116, respectively, mayadvantageously contain impregnating liquids of various concentration asfar as the impregnating agent is concerned. I

Solvent and water evaporated fromthe units 20 and condensed on the watercooled condenser 32, flows through a pipe 186 to a container 188, whereit opens below the level of an overflow pipe 190. The solvent is of suchnature that it is insoluble in water and separated therefrom by gravity.Tri-chloro-ethylene is heavier than the water and is consequentlycollected at the bottom of the container 188. A pipe 192 extendsupwardly fromthe lower part of the container 188 to a level below thatof the pipe 190 adjacent the container, and is connected to a verticalpipe 194, the upper end of which is open and drawn up to a suitablelevel. When the condensate flows into the container 188 and isseparated, the water will press solvent up in the pipe 192 and out intothe pipe 194. While the water escapes through the pipe 190 to waste thesolvent follows the pipe 194, a pipe 196 and either of two pipes 198,controlled by valves 200, to the tank 114. i

The brine passing the low temperature condenser 72 where it takes upsolvent and water, is conveyed to a tank 201 through a pipe 202controlled by a valve 204. In said tank the brine is separated from thesolvent by gravity. A pipe 206 opens at the bottom of the tank 201 wherethe solvent is collected, and another pipe 208 at a point on a higherlevel. Both said pipes may be connected to the suction side of a pump210 driven by. a motor 212. The other side of the pump 210 is through apipe 214 connected tothe pipe 104 as well as to the pipe 196. Normallybrine is pumped from the tank 201 to the heat exchanger 98 up to thecondenser 72 by the pump 210. At intervals the solvent collected in the,tank is pumped back to the tank 114 by one and the same pump, valves216, 218, 220 and 222 being provided for creating the variousconnections. The levels of the two fluids may be controlled by a levelindicator 223.

224 is a pipe, connecting the tank 116 with the interior of thecondenser 72 in order to avoid losses of solvent vapors contained in theair space of the tank, when liquid is pumped into the tank andconsequently air is expelled therefrom.

The operation of the apparatus is as follows:

After the basket 12 with a charge of units 20 is placed in position inthe chamber 10, the pump 130 is started, feeding the impregnating agentdissolved in the solvent from one of the compartments of the tank 116 tothe level 162 in the chamber 10, so that the units 20 are entirelysubmerged in the impregnating liquid. Thereafter the excess of liquid ispumped back to the tank 116. The fan 28 is now started and heat issupplied to the elements 50. The valves of the circulating system are soadjusted that substantially the whole current of air passes the channels56 and 44. During a first short period the valve 66 is opened so thatpart of the air passes the channel 58 and thus does not become heated bythe elements 50. This is V for the purpose of ensuring gradual expansionof the air. The air which is expelled from the circulating system due tothe increase of temperature thereof and evaporation of solvent from theunits 20 is forced to pass through the low temperature condenser 72 andthe container 86 where vapors of solvent following the air are condensedand thus recovered. As the circulating air becomes more saturated withvapors of the solvent, the valve 62 controlling the flow to thecondenser 32 is opened while the valve 64 is moved towards closedposition. The channel 81 is closed by the valve 60. A part .of the airand solvent vapors traversing the fan 28 thus passes the condenser 32,where the vapors vaporized from the units 20 are condensed to a partialpressure corresponding to the temperature of the condenser. The unitscontain water which is also evaporated and is also condensed on thecondenser 32. While in this way the main part of the solvent isrecovered, the units 20 and the air in the circulation system stillcontain considerable quantities thereof. Therefore the valve 60 is aftersome time opened, so that part of the circulating air after beingprecooled in the condenser 32 is-allowed to pass the low temperaturecondenser 72, whereit meets the lower ring layer 78 soaked by thebrine,'whereby the solvent vapors are absorbed to bring down the partialpressure thereof in the circulating air to the low value correspondingto the temperature of the brine. Any drops of brine following thecurrent of air upwards are'retained by the upper ring layer 80. The airis conveyed back to the channel 44 through the channel 81.

A part of the air in the apparatus is thus at this stage of the dryingoperation continuously conveyed through the low temperature condenser 72resulting in the residue of the solvent contained in the air as a wholeand in the material 20 being gradually reduced to a great extent. Thus,it has proved that the content of tri-chloro-ethylene in the units 20 isreduced to less than 1 or 2 percent counted on the weight of theimpregnated units. Thetemperature of the air when entering the chamber10 during the drying period is raised to about C. At this temperaturethe solvent not only diffuses from the units 20 and the interior oftheir sheets but is also boiled olf, whereby the time for removing thesolvent is reduced. This is of importance also from the point of viewthat a solvent as tri-chloro-ethylene has a low viscosity andconsequently penetrates into the fibres of the paper, which thereforeare thoroughly impregnatedby the bitumen. Due to the fact that themain'part of the solvent is recovered in the water condenser 32 and thatmomentarilyonly a portion of circulated air traverses the condenser 72,thecapacity of the refrigerating machine 96 can be kept Withinreasonable values. In the condenser 72 water following the air iscondensed, which isremoved together with the brine, so that there is nodeposit of ice in the condenser, a matter which otherwise wouldcomplicate the operation of the same and highly reduce its efficiency.The essential demand of cooling effect in the condenser 72 isconcentrated to a relatively short period, during which it is very high.Due to the fact that a brine is used which is circulated between theheat exchanger 98 and the tank 201, which may contain an appreciablequantity of brine, an accumulation of refrigerant is provided during theintervals between such periods which is well suited to meet theconcentrated cooling demand.

When the recovering period is finished, the basket 12 is liftedsomewhat, so that direct communication between the chamber and thesurrounding air is established. The fan 28 is kept running while thevalve 70 is opened and the passages through the condenser 32 and thechan- Y nel 56 are closed. Fresh air is now passed through the units 20cooling down the same, said air escaping to the outer atmosphere throughthe vent 68.

By varying the concentration of the bitumen in the solvent the quantityof the bitumen in the insulation may be determined at will. Forrefrigerating houses or the like it is suitable to use an insulation, inwhich the bitumen amounts to 35-60 percent of the Weight of the finishedinsulation. The percentage of the bitumen in the finished insulationwill be about the same as in the impregnating fluid.

The apparatus may be built for manufacturing 5 m. impregnated insulationor more in one charge. The fan 28 will then have to circulate about 750m. /minute to carry through the drying or recovering process within 15minutes. The condenser 72 is dimensioned for about 75,000 cal./h. whilethe momentary load may be of the 7 order of 500,000 cal./h. The airvolume enclosed by the apparatus is about 40 m.

While one more or less specific embodiment of the in veirtion has beenshown, it is to be understood that this is for purpose or illustrationonly, and the invention is not to be limited thereby, but its scope isto be determined by the appended clain'l.

What I claim is:

The method of manufacturing impregnated units of heat insulatingmaterial of the multi-ply type, which includes the steps of providing aplurality of sheets of paper secured together at spaced places to form aunit providing a multiplicity of channels of relatively small transversedimensions as compared with their length,- applying to said unit aliquid comprising a bituminous impregnating agent and a chlorinatedhydrocarbon solvent thereof, confining said unit in a suitablereceptacle forming a part of a; ductsystem having an atmospheric ventandproviding a closed circuit for circulating air, circulating andrecirculating the body of air in said circuit through said channelswhile adding heat thereto to raise the temperature of the air and thematerial to a value sufliciently high to vaporize said solvent and anymoisture inthe system and the material being treated-,- and to enhancethe impregnation of the material by the hot impregnating agent, passingthe gaseous mixture expelled through said vent due to the increase involume resulting from the heating and vaporization in heat exchangerelation with a cooling medium having a temperature below the freezingpoint of Water to condense and recover solvent from the expelled gas,continuing the re-circulation of the body of gaseous mixture throughsaid circuit and channels, while concurrently continuing to add heatthereto at one place in the circuit to maintain desired vaporizingtemperature and passing the mixture at another place in the circuit inheat exchange relation with a cooling medium to condense and recoversolvent from' the circulating gaseous mixture and thereby progressivelyreduce the solvent vapor content of the mixture and the material beingtreated, further continuing the re-circulation of the gaseous mixturewhile continuing to add heat thereto and passing at least a portion ofthe circulating body in direct contact heat exchange relation with acooling medium having a temperature below the freezing point of water tofurther condense and recover solvent until the solvent content of thecirculating body and the material being treated is substantiallyremoved, and thereafter admitting fresh air to the circuit and forcingit through said channels ata rate operative to relatively rapidly coolthe hot treated material and thereby prevent the self ignition thereof.

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